I'm still getting the impression that to get the fastest bath fill up
possible, I use a standard vented cylinder and big bore pipes. For
showering, I can get at least 2m between the base of the cold feed tank
and
the shower rose. What's your opinion ?

That would require a pump to get the sort of flow rates I'm talking about.
Also, most people like showers with pressure that you would need at least
10m head for (although some prefer low pressure as well). I like a rapid
minute bath fill. The system in my old house had mains cold and pumped hot
and could fill in under this period. My current system probably takes about
3 minutes, although it is usable after 2.

So when I say it isn't as good as the Megaflo, I'm comparing really quite
large flow rates that would satisfy almost anyone. (i.e. 40lpm vs 60lpm).

Christian.